The present invention discloses surface-active compositions for treating and dispersing oil slicks. This invention is also directed to a method for disposing of oil slicks.
Pollution of seawater by oil (crude oil or fractions of crude oil) occasioned by accidents, off-shore drilling operations, and/or discharge of ballast water or spillage from oil tankers, results in the formation of a continuous film or slick of oil which tends to continuously spread. In open seas, this oily film is undesirable because it constitutes a barrier to the transfer of air and light from the atmosphere into the seawater, which are indispensable to support marine life. In coastal waters, the oily film does damage to the crustacia beds and to the beaches.
One way of dealing with such pollution problems is to use oil dispersing compositions containing surface-active compounds. These compositions are applied on the oil slicks, generally by spraying means. They disintegrate the cohesive oily film into small droplets and disperse the droplets into the water column to a depth of several meters under the sea surface. The film is thus broken and there is again a transfer of air and light from the atmosphere. Moreover, fouling of the solid structures and beaches along the coasts is avoided.
The oil droplets which are dispersed under the sea surface are then biodegraded and consumed by micro-organisms which are living in seawater and are active in oil metabolism. This biological degradation is however a slow process and is consequently unable to prevent the settling of undegraded oil droplets and the formation of oil deposits on the floor of seas, more particularly where the water is shallow.
An active biodegradation of oil droplets needs the presence of a high amount of micro-organisms at the oil-water interface. However, these organisms are present in seawater in limited quantities. In order to stimulate the biodegradation, it is therefore necessary to speed up the proliferation of the micro-organisms. To this end, they need not only oxygen and carbon, which are present respectively in water and in polluting oils, but also nitrogen and phosphorous. Generally, the concentration of these latter two elements is very low in seawater and consequently the natural biodegradation of oil is a very slow process.
In order to increase the biodegradation rate, it has been proposed to add microbial nutrients to seawater. Mineral salts, such as ammonium salts, nitrates and phosphates, have been used. But these mineral salts are too water-soluble and have practically no affinity for the polluting oil. They are too quickly dissolved and dispersed into sea water and are not maintained at the oil-water interface where their presence is needed.
It has also been suggested to use nitrogen-containing organic nutrients which are oleosoluble, such as condensation products of urea or melamine with aldehydes. However, these organic compounds are also soluble in water. They dissociate from the oil and are dissipated into the aqueous phase. In order to overcome this disadvantage, it has been proposed to modify their solubility in water. For instance, condensation products of urea and an aldehyde containing less than four carbon atoms are first absorbed on an inert carrier and are then rendered lipophilic by coating with a paraffin or other protective colloid. These treatments require special equipment and they increase the cost of nutrients. Moreover, these latter cannot be suspended in the surface-active compositions which are used for the treatment of the oil slicks. Two separate applications, one for the surface-active composition and one for the nutrients, are therefore required. Furthermore, the coating might be quickly dissolved if the polluting oil, such as a fresh crude oil, contains aromatic hydrocarbons.
Other techniques have been suggested to reduce the solubility of the nutrients in water, but the result is compositions which only float on the water surface. These nutrients will not then promote the development of micro-organisms in the water column under the sea surface where the oil droplets are dispersed.
The difficulties encountered with prior art dispersants have been overcome by the development of new lipophilic nutrients for the micro-organisms which are present in sea waters and are active in oil degradation. These new nutrients achieve a rapid and more complete biodegradation of the oils, at low cost.